A new U.S. study found that people with the worst sleep apnoea symptoms burned 373 more calories each day than those with mild versions thereof. The authors believe that nervous system changes triggered by the condition may be to blame.

Heavy snoring is of course an annoyance for partners of the sufferer, but they can be signs of a more serious problem for the sufferer himself.

Sleep apnoea happens when the airways are partially or completely obstructed during sleep. It keeps the person (and anyone else present) from getting a good night’s rest and makes them sleepy during the day. Ties have also been found between the condition and cardiovascular and high blood pressure problems.

Scientists have been examining the link between weight gain and sleep apnoea at the University of California, San Francisco, where they measured the number of calories burned “at rest” by 212 patients, all of whom either had sleep apnoea or some other sleeping-related conditions.

The volunteers expended an average of 1,763 calories a day that way, but those with severe apnoea symptoms burned 1,999, while those with the mildest version burned 1,626 on average.

The study was published in the journal Archives of Otolaryngology – Head and Neck Surgery and lead by Dr. Eric Kezirian. It suggests that energy used by the nervous system in response to the poor quality sleep patterns experienced by heavy snorers may be to blame. Dr. Kezirian said no explanation had been given in the study for obesity and apnoea being linked.

Professor John Stradling, a sleep expert with the John Radcliffe Hospital in Oxford believes that the study’s results are “entirely plausible” and consistent with his patients’ experiences who had a hard time losing weight after their sleep apnoea symptoms were treated.

''I used to joke that sleep apnoea was free exercise at night - it's nice to have that confirmed,'' Stradling said.

Three possible reasons were found for why sufferers burn more calories at night.

First off, they spend less time in a state of deep sleep, during which the body temperature naturally drops, they could also spend more energy just trying to breathe, not to mention that each time their sleep is interrupted by these breathing problems, their nervous systems would fire a dose of adrenaline, which burned more calories. The ultimate cause of the calorie loss for sufferers of apnoea is currently unknown however, and subject to further studies.

Stradling warned that other effects of sleep apnoea made it not a very good way to lose weight:

''If you have sleep apnoea, you are very sleepy during the day, and demotivated to do any exercise - we also know that sleep deprivation increases appetite and decreases willpower.''